When you venture out into the wilderness, most of the time all you want to do is completely disconnect from the rest of the world, but all too often, that's just not an option. When you can't afford to be completely off the grid, but know you'll still need to recharge your gadgets, throw the FlameStower ($60) into your pack. All it needs to generate enough electricity to charge the batteries of your USB-connected devices is the heat from your camping or cook fire. Lightweight and reliable, it works by conducting heat to a thermoelectric generator, which is in contact with a water reservoir — the combination of hot and cold produces enough juice to charge your device in as little as three hours.